Network Working Group G. Klyne
Internet-Draft MIMEsweeper Group
Expires: July 30, 2002 M. Nottingham
J. Mogul
Compaq WRL
Jan 29, 2002
Registration procedures for message headers
draft-klyne-msghdr-registry-02
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
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This Internet-Draft will expire on July 30, 2002.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This specification defines registration procedures for the message
headers used by Internet mail, HTTP, news and other applications.
Discussion of this document
Please send comments to <ietf-822@imc.org>. To subscribe to this
list, send a message with the body 'subscribe' to <ietf-822-
request@imc.org>.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Structure of this document . . . . . . . . . . . . . . . . . 4
1.2 Document terminology and conventions . . . . . . . . . . . . 4
2. Message headers . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Standard and non-standard headers . . . . . . . . . . . . . 4
2.2 Definitions of message headers . . . . . . . . . . . . . . . 5
2.2.1 Application-specific message headers . . . . . . . . . . . . 5
3. Registration procedure . . . . . . . . . . . . . . . . . . . 6
3.1 Header specification . . . . . . . . . . . . . . . . . . . . 6
3.2 Registration templates . . . . . . . . . . . . . . . . . . . 7
3.2.1 Normative header template . . . . . . . . . . . . . . . . . 7
3.2.2 Provisional header template . . . . . . . . . . . . . . . . 7
3.3 Submission of registration . . . . . . . . . . . . . . . . . 8
3.4 Change control . . . . . . . . . . . . . . . . . . . . . . . 8
3.5 Comments on header definitions . . . . . . . . . . . . . . . 9
3.6 Location of message header registry . . . . . . . . . . . . 9
4. IANA considerations . . . . . . . . . . . . . . . . . . . . 9
5. Security considerations . . . . . . . . . . . . . . . . . . 9
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
References . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 13
A. Revision history . . . . . . . . . . . . . . . . . . . . . . 14
A.1 draft-klyne-msghdr-registry-02 . . . . . . . . . . . . . . . 14
A.2 draft-klyne-msghdr-registry-01 . . . . . . . . . . . . . . . 14
A.3 draft-klyne-msghdr-registry-00 . . . . . . . . . . . . . . . 15
B. Todo . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Full Copyright Statement . . . . . . . . . . . . . . . . . . 16
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1. Introduction
This specification defines registration procedures for the message
headers used by Internet mail, HTTP, newsgroup feeds and other
Internet applications.
Benefits of a central registry for message headers include:
o providing a single point of reference for standardized headers;
o providing a central point of discovery for established headers,
and easy location of their defining documents;
o discouraging multiple definitions of a header name for different
purposes;
o helping those proposing new headers discern established trends and
conventions, and avoid names that might be confused with existing
ones;
o encouraging convergence of header name usage across multiple
applications/protocols.
The primary specification for Internet message headers in email is
the Internet mail message format specification, RFC 2822 [34].
HTTP/1.0 [7] and HTTP/1.1 [28] define message headers (respectively,
the HTTP-header and message-header protocol elements) for use with
HTTP. These specifications also define a number of headers, and and
provide for extension through the use of new field-names.
There are many other Internet standards track documents that define
additional headers for use within the same namespaces, notably MIME
[8] and related specifications. Other Internet applications that use
MIME, such as newsgroup feeds (RFC 1036 [1]) may also use many of the
same headers.
Although in principle each application defines its own set of valid
headers, exchange of messages between applications (e.g. mail to
news gateways), common use of MIME encapsulation, and the possibility
of common processing for various message types (e.g. a common
message archive and retrieval facility) makes it desirable to have a
single point of reference for standardized and proposed headers.
Listing headers together reduces the chance of an accidental
collision, and helps implementers find relevant information. The
message header registries defined here serve that purpose.
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1.1 Structure of this document
Section Section 2 discusses the purpose of this specification, and
indicates some sources of information about defined message headers.
Section Section 3 defines the message header registry, and sets out
requirements and procedures for creating entries in it.
1.2 Document terminology and conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [14].
NOTE: indented comments like this provide additional nonessential
information about the rationale behind this document.
[[[Editorial comments and questions about outstanding issues are
provided in triple brackets like this. These working comments should
be resolved and removed prior to final publication.]]]
2. Message headers
2.1 Standard and non-standard headers
Many message headers are defined in standards-track documents, which
means they have been subjected to a process of community review and
achieved consensus that they provide a useful and well-founded
capability. Many other headers have been defined and adopted ad-hoc
to address a locally occurring requirement; some of these have found
widespread use.
The registries defined here are intended to cater for all of these
headers, while maintaining a clear distinction and status for those
which have community consensus. To this end, two registries are
defined:
o Normative Message Headers, intended for headers defined in IETF
standards-track documents, or those that have achieved a
comparable level of community review. The assignment policy for
such registration is "IETF Consensus", as defined by RFC 2434
[26].
o Provisional Message Headers, intended for any header proposed by
any developer, without making any claim about the usefulness
quality of its definition. The assignment policy for registration
of these is "Private Use", per RFC 2434 [26].
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Neither registry tracks the syntax, semantics or type of field-
values. Only the field-names and applicable protocols are
registered; all other details are specified in the defining documents
referenced by registry entries. Significant updates to such
references (e.g., the replacement of a Proposed Standard RFC by a
Draft Standard RFC, but not the revision of an Internet-Draft) SHOULD
be accompanied by updates to the corresponding registry entries.
Note that there exist at least two other sources information about
message headers:
o RFC 2076 [11], as updated [40], contains a list of commonly used
message headers, and
o Dan Bernstein maintains a list of standard and non-standard mail
message headers [41].
2.2 Definitions of message headers
RFC 2822 [34] defines a general syntax for message headers, and also
defines a number of headers for use with Internet mail. HTTP/1.0 [7]
and HTTP/1.1 [28] do likewise for HTTP. Additional header names are
defined in a variety of standards-track RFC documents, including: RFC
1036 [1], RFC 1496 [2], RFC 1505 [3], RFC 1766 [5], RFC 1864 [6], RFC
2156 [16], RFC 2183 [17], RFC 2045 [8], RFC 2046 [8], RFC 2109 [12]
(obsoleted by RFC 2965), RFC 2110 [13], RFC 2227 [18], RFC 2298 [20],
RFC 2369 [23], RFC 2421 [25], RFC 2518 [27], RFC 2617 [29], RFC 2821
[33], RFC 2912 [36], RFC 2919 [37], and RFC 2965 [38].
2.2.1 Application-specific message headers
Internet applications that use message headers include Internet mail
[33][34], NNTP newsgroup feeds [1], HTTP web access [28] and any
other that uses MIME [8] encapsulation of message content.
In some cases (notably HTTP [28]), the header syntax and usage is
redefined for the specific application. This registration is
concerned only with the allocation and specification of header names,
and not with the details of header implementation in specific
protocols.
In some cases, the same header name may be specified differently (by
different documents) for use with different application protocols;
e.g. The Date: header used with HTTP has a different syntax than the
Date: header used with Internet mail. In other cases, a header name
may have a common specification across multiple protocols (ignoring
protocol-specific lexical and character set conventions); e.g. this
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is generally the case for MIME headers with names of the form
'Content-*'.
Thus, we need to accommodate application-specific headers, while
wishing to recognize and promote (where appropriate) commonality of
other headers across multiple applications. Common registries are
used for all applications, and each registered header specifies the
application protocol for which the registered definition applies. A
given header name may have multiple registry entries for different
protocols; in the Normative Message Headers registry, a given header
name may be registered only once for any given protocol.
3. Registration procedure
The procedure for registering a message header is:
1. Construct a header specification
2. Prepare a registration template
3. Submit the registration template
3.1 Header specification
Registration of a new message header starts with construction of a
proposal that describes the syntax, semantics and intended use of the
header. For normative headers, this proposal MUST be published as an
RFC.
A registered header name MUST conform at least to the syntax defined
by RFC 2822, section 3.6.8, for "field name".
Further, the "." character is reserved to indicate a naming sub-
structure and MUST NOT be included in any registered header name.
Currently, no specific sub-structure is defined; if used, any such
structure MUST be defined by a standards track RFC document.
It is further RECOMMENDED that characters in a registered message
header name are restricted to those characters that can be used
without escaping in a URI [24] or URN [15], namely upper- or lower-
case ASCII letters, decimal digits, "(", ")", "+", ",", "-", "=",
"@", ";", "$", "_", "!", "*" and "'". Of course, a header name must
also conform to any applicable rules of the protocol(s) with which it
is used. Many headers names may find some use in conjunction with
XML [39], in which case the name characters should be further
restricted to just letters, digits, hyphen ('-') and underscore ('_')
characters, with the first character being a letter or underscore.
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3.2 Registration templates
The registration template for a message header may be contained in
the defining document, or prepared separately.
3.2.1 Normative header template
An header registered as a Normative Message Header MUST be defined
according to "IETF Consensus" rules (per RFC 2434 [26]), and MUST
have a name which is unique among all the Normative Message Headers
that may be used with the same application protocol. The header name
MUST NOT start with "X-" or "x-".
The registration template has the following form.
NORMATIVE HEADER REGISTRATION TEMPLATE:
Header field name:
The name requested for the new header. This MUST conform to the
header specification details above.
Applicable protocol:
Specify "mail", "http", "news", or cite any other standards-track
RFC defining the protocol with which the header is intended to be
used.
Specification document(s):
Reference to the RFC(s) that specify the header for use with the
indicated protocol. An indication of the relevant sections MAY
also be included, but is not required.
Related information:
Optionally, citations to additional documents containing further
relevant information.
3.2.2 Provisional header template
Registration as a Provisional Message Header does not imply any kind
of endorsement by the IETF, IANA or any other body.
The only requirement for a header to be registered as a Provisional
Message Header is that it MUST have a citable specification.
The registration template has the following form.
PROVISIONAL HEADER REGISTRATION TEMPLATE:
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Header field name:
The name requested for the new header. This SHOULD conform to the
header specification details above.
Applicable protocol:
Specify "mail", "http", "news", or cite any other standards-track
RFC defining the protocol with which the header is intended to be
used.
Specification document(s):
Reference to document(s) that specifies the header for use with
the indicated protocol. An indication of the relevant sections
MAY also be included, but is not required.
Author/Change controller:
The name and email address of the author, and person who may
authorize changes to or retraction of the registration.
Related information:
Optionally, citations to additional documents containing further
relevant information.
3.3 Submission of registration
The registration is submitted for incorporation in the IANA message
header registry by one of the following means:
o An IANA considerations section in a defining RFC, calling for
registration of the message header and referencing the
registration template within the same document. Registration of
the header is processed as part of the RFC publication process.
o Sending the registration template in an email to the designated
email address [45]. IANA will register the message header if the
requested name and the specification document meet the criteria
stated.
3.4 Change control
Change control of a header registration is subject to the same
condition as the initial registration; i.e. publication of an IESG-
approved RFC for a Normative Message Header, or on request of the
indicated author/change controller for a Provisional Message Header.
In addition, a change to or retraction of Provisional Message Header
registration may be requested by the IESG.
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It is intended that entries in the Normative Header Registry may be
used in the construction of URNs (per RFC 2141 [15]) which have
particular requirements for uniqueness and persistence (per RFC 1737
[4]). Therefore, once an entry is made in the Normative Message
Header registry, the combination of the header name and applicable
protcol MUST NOT subsequently be registered for any other purpose.
(This is not to preclude revision of the applicable specification(s)
within the appropriate IETF Consensus rules, and corresponding
updates to the specification citation in the header registration.)
3.5 Comments on header definitions
Comments on proposed message headers should preferably be sent to the
discusion forum for the protocol specification concerned. They may
also be sent to the IETF-822 list [45] if they concern wider
implications than are addressed by the protocol header specification
document.
3.6 Location of message header registry
The message header registry is accessible from IANA's web site [46].
4. IANA considerations
This specification calls for:
o A new IANA registry for normative message headers per section
Section 3 of this document. The policy for inclusion in this
registry is described in sections Section 3.1 and Section 3.2.1.
o A new IANA registry for provisional message headers per section
Section 3 of this document. The policy for inclusion in this
registry is described in sections Section 3.1 and Section 3.2.2.
Initial header registrations are provided by the following companion
documents:
o For mail message headers: Registration of mail header fields [42]
o For HTTP message headers: Registration of HTTP header fields [43]
5. Security considerations
No security considerations are introduced by this specification
beyond those already inherent in the use of message headers.
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6. Acknowledgements
The authors gratefully acknowledge the contribution of those who
reviewed earlier versions of this memo: Charles Lindsey, [[[...]]]
References
[1] Horton, M. and R. Adams, "Standard for interchange of USENET
messages", RFC 1036, December 1987.
[2] Alvestrand, H., Jordan, K. and J. Romaguera, "Rules for
downgrading messages from X.400/88 to X.400/84 when MIME
content-types are present in the messages", RFC 1496, August
1993.
[3] Costanzo, A., Robinson, D. and R. Ullmann, "Encoding Header
Field for Internet Messages", RFC 1505, August 1993.
[4] Masinter, L. and K. Sollins, "Functional Requirements for
Uniform Resource Names", RFC 1737, December 1994.
[5] Alvestrand, H., "Tags for the Identification of Languages", RFC
1766, March 1995.
[6] Myers, J. and M. Rose, "The Content-MD5 Header Field", RFC
1864, October 1995.
[7] Berners-Lee, T., Fielding, R. and H. Nielsen, "Hypertext
Transfer Protocol -- HTTP/1.0", RFC 1945, May 1996.
[8] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
[9] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, November
1996.
[10] Fielding, R., Gettys, J., Mogul, J., Nielsen, H. and T.
Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC
2068, January 1997.
[11] Palme, J., "Common Internet Message Headers", RFC 2076,
February 1997.
[12] Kristol, D. and L. Montulli, "HTTP State Management Mechanism",
RFC 2109, February 1997.
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[13] Palme, J. and A. Hopmann, "MIME E-mail Encapsulation of
Aggregate Documents, such as HTML (MHTML)", RFC 2110, March
1997.
[14] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[15] Moats, R., "URN Syntax", RFC 2141, May 1997.
[16] Kille, S., "MIXER (Mime Internet X.400 Enhanced Relay): Mapping
between X.400 and RFC 822/MIME", RFC 2156, January 1998.
[17] Moore, K., Troost, R. and S. Dorner, "Communicating
Presentation Information in Internet Messages: The Content-
Disposition Header Field", RFC 2183, August 1997.
[18] Mogul, J. and P. Leach, "Simple Hit-Metering and Usage-Limiting
for HTTP", RFC 2227, October 1997.
[19] Holtman, K. and A. Mutz, "Transparent Content Negotiation in
HTTP", RFC 2295, March 1998.
[20] Fajman, R., "An Extensible Message Format for Message
Disposition Notifications", RFC 2298, March 1998.
[21] Holtman, K., "The Safe Response Header Field", RFC 2310, April
1998.
[22] Masinter, L., "Hyper Text Coffee Pot Control Protocol
(HTCPCP/1.0)", RFC 2324, April 1998.
[23] Baer, J. and G. Neufeld, "The Use of URLs as Meta-Syntax for
Core Mail List Commands and their Transport through Message
Header Fields", RFC 2369, July 1998.
[24] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.
[25] Parsons, G. and G. Vaudreuil, "Voice Profile for Internet Mail
- version 2", RFC 2421, September 1998.
[26] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October
1998.
[27] Goland, Y., Whitehead, E., Faizi, A., Carter, S. and D. Jensen,
"HTTP Extensions for Distributed Authoring -- WEBDAV", RFC
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2518, February 1999.
[28] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
[29] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A. and L. Stewart, "HTTP Authentication:
Basic and Digest Access Authentication", RFC 2617, June 1999.
[30] Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
August 1999.
[31] Rescorla, E. and A. Schiffman, "The Secure HyperText Transfer
Protocol", RFC 2660, August 1999.
[32] Nielsen, H., Leach, P. and S. Lawrence, "An HTTP Extension
Framework", RFC 2774, February 2000.
[33] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April
2001.
[34] Resnick, P., "Internet Message Format", RFC 2822, April 2001.
[35] Herriot, R., Butler, S., Moore, P., Turner, R. and J. Wenn,
"Internet Printing Protocol/1.1: Encoding and Transport", RFC
2910, September 2000.
[36] Klyne, G., "Indicating Media Features for MIME Content", RFC
2912, September 2000.
[37] Chandhok, R. and G. Wenger, "List-Id: A Structured Field and
Namespace for the Identification of Mailing Lists", RFC 2919,
April 2001.
[38] Kristol, D. and L. Montulli, "HTTP State Management Mechanism",
RFC 2965, October 2000.
[39] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler,
"Extensible Markup Language (XML) 1.0 (2nd ed)", W3C
Recommendation xml, October 2000,
<http://www.w3.org/TR/2000/REC-xml-20001006>.
[40] Palme, J., "Common Internet Message Header Fields", Internet
draft draft-palme-mailext-headers-05, May 2001,
<http://search.ietf.org/internet-drafts/draft-palme-mailext-
headers-05.txt>.
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[41] Bernstein, D., "Internet mail field name index",
<http://cr.yp.to/immhf/index.html>.
[42] Klyne, G., "Registration of mail header fields", Internet draft
[[[draft-klyne-hdrreg-mail-00]]], Jan 2002,
<[[[http://search.ietf.org/internet-drafts/draft-klyne-hdrreg-
mail-00.txt]]]>.
[43] Nottingham, M. and J. Mogul, "Registration of HTTP header
fields", Internet draft [[[draft-nottingham-hdrreg-http-00]]],
Jan 2002, <[[[http://search.ietf.org/internet-drafts/draft-
nottingham-hdrreg-http-00.txt]]]>.
[44] Feldmann, A., "Usage of HTTP header fields", December 1998,
<http://www.research.att.com/~anja/w3c_webchar/http_header.html>
.
[45] "Mail address for submission of header registration template",
<mailto:[[[ietf-message-headers]]]@iana.org>.
[46] "IANA list of registered message headers",
<http://www.iana.org/[[[ToBeDefined]]]>.
Authors' Addresses
Graham Klyne
MIMEsweeper Group
1310 Waterside
Arlington Business Park
Theale, Reading RG7 4SA
UK
Phone: +44 118 903 8000
Fax: +44 118 903 9000
EMail: Graham.Klyne@MIMEsweeper.com
Mark Nottingham
EMail: mnot@pobox.com
URI: http://www.mnot.net/
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Jeffrey C. Mogul
Western Research Laboratory, Compaq Computer Corporation
250 University Avenue
Palo Alto, CA 94305
US
Phone: 1 650 617 3304 (email preferred)
EMail: JeffMogul@acm.org
Appendix A. Revision history
[[[Please remove this section on final publication]]]
A.1 draft-klyne-msghdr-registry-02
02a 22-Jan-2002:
* Merged with HTTP header registry proposal.
* Move initial registrations to separate documents.
02b 29-Jan-2002:
* Editorial revisions.
A.2 draft-klyne-msghdr-registry-01
01a 04-Jan-2002:
* In response to feedback from interested parties, expanded the
registry to cover Normative and Provisional message header
registrations.
* Defined a formal role for the applicable protocol(s) in the
registry: the combination of header name and any applicable
protocol must be unique for a Normative Message Header.
* Noted further constraints to the header name format for XML
name compatibility.
* Fixed registration policy for a Normative Message Header to be
"IETF Consensus".
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A.3 draft-klyne-msghdr-registry-00
00a 27-Sep-2001:
* Document initially created.
Appendix B. Todo
[[[Please remove this section on final publication]]]
o Finalize references to initial registrations.
o Finalize email address for submission of registration templates.
o Finalize web address for registry.
o Confirm that IANA are comfortable with the proposed procedures.
In particular the uniqueness requirements on registry entries.
o Consider the following comment about X-headers: we may need to do
that protocol-by-protocol; IIRC their status is different in HTTP
than in mail, for example. In the case of HTTP, I don't think X-
headers should be encouraged; however, I can see documenting
current X- headers. The trick is distinguishing between current
and new. If we don't take X-headers, it sends the message that
they shouldn't be used because you can't check the status of them.
o Consider whether provisions to prevent abuse are OK. Currently,
IESG can override any registration. One alternative proposed was
to have IESG-appointed domain expert review of all registrations.
o Should the controller of a registration always be the author of
the corresponding specification.
o Confirm this is OK: no change controller is specified for
normative headers because these are effectively under control of
IESG, by virtue of being specified by an IESG-approved RFC.
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Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
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or assist in its implementation may be prepared, copied, published
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Acknowledgement
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